Sort Numeric Strings in a List - Python

We are given a list of numeric strings and our task is to sort the list based on their numeric values rather than their lexicographical order. For example, if we have: a = ["10", "2", "30", "4"] then the expected output should be: ["2", "4", "10", "30"] because numerically, 2 < 4 < 10 < 30.

Using sorted()

We use Python's built-in sorted() function along with the key=int parameter as this converts each element to an integer for comparison during sorting.

a = ["10", "2", "30", "4"]

# Sort the list by converting each element to int during comparison
res = sorted(a, key=int)
print(res)

['2', '4', '10', '30']

Explanation:

• key=int argument tells sorted() to convert each string to an integer before comparing them ensuring numerical order.
• sorted list res contains the numeric strings arranged as ["2", "4", "10", "30"].

Using list.sort()

We sort the list in-place using the sort() method with the same key=int parameter.

a = ["10", "2", "30", "4"]

# In-place sorting using key=int
a.sort(key=int)
print(a)

['2', '4', '10', '30']

Explanation:

• sort() method modifies the original list, like Method 1 key=int ensures that the elements are compared as integers.
• original list a is updated to ["2", "4", "10", "30"].

Naive Approach Using Nested Loops

We implement a selection sort (or bubble sort) by using nested loops that compare elements by converting them to integers during each comparison.

a = ["10", "2", "30", "4"]

# Naive approach: using nested loops to sort the list in-place
for i in range(len(a)):
    for j in range(i + 1, len(a)):
        if int(a[i]) > int(a[j]):
            a[i], a[j] = a[j], a[i]

print(a)

['2', '4', '10', '30']

Explanation:

• For each element, the inner loop compares it with every subsequent element and int() conversion happens during each comparison to ensure numerical order.
• If an element is found to be greater than a later element (numerically) then they are swapped.